Electronic Beam Steering and Polarization Agile Planar Antennas in Liquid Crystal Technology

IEEE Trans. Microwave Theory Techn.

Bachiller

et al. 2019

Liquid Crystal (LC) is an anisotropic liquid material which flows like a liquid, but at the same time its molecules have an orientational order like in the solid state. Thus, LC is a promising dielectric material for designing reconfigurable devices at microwave frequencies. In order to optimize the design of reconfigurable microwave devices, accurate values of the dielectric permittivity and the loss tangent of LCs are needed. However, new LCs are not well characterized at these frequencies because of its recent use for microwave applications. Therefore, the characterization in this frequency range is required for its practical use within microwave components and devices.In this work, a split-cylinder resonator method is used for the characterization of four different nematic LCs at two frequency points, i.e. 5 and 11 GHz. This characterization includes the extraction of their complex dielectric permittivity values at these frequencies. The employed method allows to obtain the two extreme permittivity values without applying any external electric or magnetic field to polarize the LC molecules. Two different approaches, a modal analysis method and a full-wave numerical technique have been used for determining the LC parameters obtaining similar results in both cases.

Section: Liquid Crystal Samplesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Characterization of Nematic Liquid Crystal at Microwave Frequencies Using Split-Cylinder Resonator Method

Sánchez

IEEE Trans. Microwave Theory Techn.

Bachiller

et al. 2019

“…The dielectric permittivity values of the nematic LCs are defined by the angle formed between the director vector and an external RF electric field ⃗ . The values represented by and || are, respectively, the permittivity values when ⃗ is perpendicular and parallel to ⃗ [5]. Moreover, loss tangents and || are also defined corresponding to those directions.…”

Section: Introductionmentioning

confidence: 99%

Measurement of the Dielectric Properties of Liquid Crystal Material for Microwave Applications

Sánchez

Proceedings 17th International Conference on Microwave and High Frequency Heating

Martín

et al. 2019

Liquid Crystal (LC) is an anisotropic liquid material which flows like a liquid, but at the same time its molecules have an orientational order like in the solid state [1]. Thus, LC is a promising dielectric material for designing reconfigurable devices at microwave frequencies. In order to optimize the design of reconfigurable microwave devices, accurate values of the dielectric permittivity and the loss tangent of LCs are needed. However, new LCs are not well characterized at these frequencies because of its recent use for microwave applications. Therefore, the characterization in this frequency range is required for its practical use within microwave components and devices [2]. In this work, the split-cylinder resonator method has been used for the characterization of LCs at two frequency points, i.e. 5 and 11 GHz. The method is based on the measurement of the resonance frequency and quality factor of the two states of the LC molecules for extracting the complex dielectric permittivity [3]. For achieving these two states, no electric or magnetic fields are needed, just the cell must be turned 90º inside the cavity. The dielectric properties (permittivity and loss tangent) of four different LC samples, GT3-23002 from Merck and QYPD193, QYPD142, and QYPD036 from Qingdao QY Liquid Crystal Co, have been obtained. The highest values of the dielectric anisotropy are presented for the samples QYPD036 and QYPD193, together with the highest values of the corresponding loss tangent parameters. Furthermore, it is observed for all the LCs that the loss tangent decreases and the dielectric anisotropy increases at higher frequencies, which must be taken into account in the development of reconfigurable microwave devices.

“…This promising technology could even be used in a reconfigurable scheme, since the coaxial line has two conductors, on which a DC bias voltage can be applied. For reconfiguration purposes lumped elements [12], [13] or anisotropic materials [14], [15] are used.…”

Section: Introductionmentioning

confidence: 99%

Miniaturization of Power Divider and 90° Hybrid Directional Coupler for C-Band Applications Using Empty Substrate-Integrated Coaxial Lines

Merello

IEEE Trans. Microwave Theory Techn.

Bachiller

et al. 2018

This work presents the practical realization of a power divider and a 90 • hybrid directional coupler in Empty Substrate Integrated Coaxial Line (ESICL) for C-band frequency applications. This new type of transmission line is very promising in terms of electric performance, bandwidth, integration with other planar circuits and manufacturing simplicity. The ESICL has been designed for obtaining a wide monomode bandwidth with a characteristic impedance of 50 ohms. Furthermore, an improvement of the efficient transition between the ESICL and the Grounded Coplanar Waveguide (GCPW), used as feeding line, has been also proposed. The passive devices built using this technology are reduced in mass and volume, keeping robustness and providing a well balanced power division, as well as reduced losses and high isolation in the whole operational bandwidth. Two prototypes have been manufactured and the experimental results are in good agreement with the simulated designs. Index Terms-C-band, empty substrate integrated coaxial line (ESICL), ESICL broadband transition, power divider, hybrid directional coupler.